Abstrict
The invention relates to a filter cloth for a filter, which has
a supporting surface, comprising a fixing area for attachment to
the filter and a filtration area for resting on the supporting surface.
In order to raise the filtration area from the supporting surface
an extensible fabric structure is provided at least in the filtration
area, with highly elastic monofilament threads being selectively
incorporated into the fabric structure at least in the filtration
area in order to produce a defined amount of elasticity.
Claims
1. Filter cloth for a filter, which has a supporting surface, comprising
a fixing area for attachment to the filter and a filtration area
for resting on the supporting surface, characterized in that an
extensible fabric structure is provided at least in the filtration
area to raise the filtration area from the supporting surface and
in that highly elastic monofilament threads are incorporated selectively
into the fabric structure at least in the filtration area to produce
a defined amount of elasticity.
2. Filter cloth according to claim 1, characterized in that the
filtration area is designed in an inflatable manner, the extension
being greater than that of an accumulated filter cake.
3. Filter cloth according to any one of claims 1 or 2, characterized
in that the fabric structure has at least one further thread with
a low elasticity so that during the inflation a defined relative
movement occurs between the threads of different elasticity.
4. Filter cloth according to any one of claims 1 to 3, characterized
in that the highly elastic monofilament thread is produced of polyester,
polyurethane, polyolefins, polyamides and/or their copolymers, in
particular copolyether-ester.
5. Filter cloth according to any one of claims 1 to 4, characterized
in that in addition to monofilament threads the fabric structure
also has elastic and/or regular non-elastic multifilament and/or
quasi-multifilament threads.
6. Filter cloth according to any one of claims 1 to 3 or 5, characterized
in that the warps of the fabric structure consist of a highly elastic
monofilament thread and the wefts consist of a regular non-elastic
thread.
7. Filter cloth according to any one of claims 1 to 6, characterized
in that a surface of the filter cloth, in particular the surface
of a side facing towards a filter cake, is calendered and/or provided
with a coating for the refinement of the surface.
8. Filter cloth according to any one of claims 1 to 7, characterized
in that the fabric structure has twill and/or satin weaves.
9. Filter bag for disk filters, which is produced from a filter
cloth according to any one of claims 1 to 8.
10. Filter cloth for a filter cake forming filtration with a filtration
area, which has an extensible fabric structure with a highly elastic
monofilament thread, characterized in that the fabric structure
has at least one further thread with an elasticity that is lower
than that of the highly elastic monofilament thread, that the fabric
structure consisting of the highly elastic monofilament thread and
the further thread is designed with a defined amount of elasticity,
which permits a greater extension than that of the formed filter
cake, and in that the elasticity of the highly elastic monofilament
thread and of the at least one further thread is selected to be
different in such a manner that during the extension a defined relative
movement occurs between the threads of different elasticity.
Description [0001] The invention relates to a filter cloth for a filter according
to the preamble of claim 1 and to a filter bag for a disk filter
according to claim 9.
[0002] A filter cloth according to the preamble has a fixing area
for attachment to the filter and a filtration area for resting on
a supporting surface of the filter.
[0003] Such a filter cloth is employed for example in vacuum and
pressure disk filters that are used for the liquid-solid separation
mainly in ore and mineral mines, for instance for refining processes.
[0004] In a disk filter a plurality of disks are arranged on a
tubular axis, which are each divided into a plurality of segments
with cavities. These segments are covered with substantially trapezoidal
bags of filter fabric through which the liquid-solid separation
takes place. During the operation the filter disks are immersed
up to approximately one third of their diameter in a suspension
that is to be filtered and may be contained for instance in a tank,
a tub or a trough. The filter disks can be rotated gradually or
continuously by means of the tubular, hollow axis. The cavities
of the individual disk segments of a filter disk are connected to
each other and a vacuum is applied thereto during the operation.
The vacuum causes the suspension fluid to pass from the tank into
the cavities, while a proportion of the solid matter in the suspension
to be filtered is retained by the filter fabric and forms a so-called
filter cake. The proportion of liquid of the suspension, which has
passed through the filter fabric, is remove from the filter by a
pump.
[0005] In a continuous operation the filter cake must be detached
gradually or continuously from the filter fabric, since the solid
matter would otherwise be reconveyed into the suspension reservoir.
It is known that this detachment of the filter cake is effected
by means of a stripper arranged on the periphery of the filter cloths.
However, in most cases this leads to a very strong mechanical stress
of the filter cloth. For example roughenings can be caused by the
mechanical contact of a stripper with the filter fabric, which foster
a clogging of the filter fabric as a result of the inclusion of
small particles and therefore lead to a progressive loss in efficiency
of the filter cloth.
[0006] It is also known that the filter cloth is provided in one
or several directions with threads that are particularly stable,
for example metal wires too, in order to protect the filter cloth
against mechanical stress occurring during the stripping process.
However, the effort involved in the production of such filter cloths
is increased considerably through this and consequently their costs
too.
[0007] Another known and basically different method for detaching
the filter cake from the filter cloth in a disk filter is to interrupt
the vacuum in a filter disk segment in a particular angular position
and to blow the filter cake off the filter cloth by means of a blast
of air. The blown off solid matter can be collected by a funnel
and removed from the filter by means of suitable devices.
[0008] If a filter disk rotates for instance in the clockwise direction,
the filter cake must be detached from the disk at an angular position
corresponding to the time of "three o'clock", as the solid
matter would otherwise be reconveyed into the suspension reservoir.
To this end the vacuum is interrupted for example at the angular
position of "three o'clock" and air is blown into the
filter disk segment. Through the blast of air the filter cake is
detached from the filter cloth, collected by means of a funnel and
removed from the filter.
[0009] For the production of elastic filter fabrics or elastic
fabrics that are known so far textured, i.e. crimped multifilament
threads are used. However, such fabrics consisting of multifilament
threads have a number of disadvantages. On account of the very large
surface of crimped multifilament threads the inclusion of small
particles into the fabric structure is fostered, which leads to
a gradual clogging of the filter fabric and thus to a gradual loss
in efficiency during the operation.
[0010] Moreover, included particles also cause a deterioration
of e elastic properties of the filter fabric. In addition, a filter
fabric consisting of a plurality of fine individual fibres in textured
threads has poor abrasive properties by nature, since mechanical
influences may lead very quickly to a damage of the very fine threads.
Finally, the very strong structuring of the fabric surfaces resulting
from the textured multifilament threads brings about a very strong
adherence of the filter cake to the fabric surface.
[0011] The object of the invention is to provide a filter cloth
and a filter bag, in which a filter cake can be detached or removed
in a particularly simple and gentle manner, which are particularly
easy to clean and in addition have a particularly long service life.
[0012] This object is solved by a filter cloth having the features
of claim 1 and by a filter bag according to claim 9.
[0013] Preferred embodiments of the filter cloth are claimed in
the subclaims.
[0014] A filter cloth of the above-stated type is improved according
to the invention in that an extensible fabric structure is provided
at least in the filtration area in order to raise the filtration
area from the supporting surface and that highly elastic monofilament
threads are selectively incorporated into the fabric structure at
least in the filtration area in order to produce a defined amount
of elasticity.
[0015] A basic idea of the invention may be seen in the fact that
highly elastic monofilament threads are incorporated into at least
a portion of the filter cloth so that in this fabric portion a specific
desired amount of elasticity and consequently a desired behaviour
of the filter cloth, in particular a strong extension, is given
when introducing a blast of compressed air into the particular cavity
of a disk filter segment.
[0016] Due to the fact that the monofilament threads have very
smooth surfaces the adherence to the filter cake is reduced appreciably
in the filter cloth according to the invention, from which follow
altogether excellent cake removing properties. Furthermore, on account
of the very smooth surface of the monofilament threads the inclusion
of small particles in the fabric structure is reduced considerably
so that monofilament fabrics show a distinctly lower clogging tendency
and in addition they can be cleaned and/or de-clogged better. When
introducing the reverse blast of air for the removal of the cake
for example, i.e. when introducing a blast of compressed air, remaining
amounts of fine particles that are present in the filter fabric
can also be blown off at the same time.
[0017] Another fundamental advantage of the filter cloth according
to the invention may be seen in the fact that monofilament elastic
fabrics have a significantly lower elastic fatigue than multifilament
elastic fabrics. This means that monofilament elastic fabrics retain
their form-recovering properties over a longer period of time and
that fabric deformations resulting from permanent overextensions
can be avoided. Thus, a wrinkling of the fabric and consequently
a premature breakage of the fabric can be prevented.
[0018] Finally, with respect to the abrasive resistance the filter
cloth according to the invention also shows significant improvements
in comparison to fabrics consisting of multifilament elastic threads.
[0019] In an advantageous embodiment of the invention the fabric
structure is designed in an inflatable manner in the filtration
area. In particular a balloon-like inflation can be provided. Here
the detachment of the filter cake is not only effected by the exhaust
air but also by the considerable extension of the filter cake surface.
The extension can be chosen to range between 2% and 80%, with this
extension being greater than that of the filter cake. Through this
a tearing up and a detaching of the filter cake is fostered. Furthermore,
an additional self-cleaning of the filter cloth can be achieved
as a result of a balloon effect, the cause of this self-cleaning
effect being a fulling process that takes place between adjoining
threads in the filter cloth, i.e. a relative movement of adjoining
threads. Through this especially the solid particles that accumulate
on the crossing points of the threads are detached and stripped
off.
[0020] To this end it is particularly advantageous that the fabric
structure has at least one further thread with a low elasticity
and that during the inflation a defined relative movement takes
place between the threads of different elasticity. The use of threads
that have a different elasticity inevitably results in comparatively
great relative movements between the fibres, whereby the self-cleaning
effect of the filter cloth is intensified. By preference, the ratio
of elasticity of the different threads is 2 to 1 and higher.
[0021] The highly elastic monofilament thread is preferably made
of polyester, polyurethane, polyolefins, polyamides and/or their
copolymers, in particular copolyether-ester. As far as especially
copolyether-ester is concerned this is a synthetic copolymer which
has excellent properties with regard to strength, elongation at
break, knot strength and especially with regard to elastic endurance
for being used in a filter cloth in accordance with the invention.
[0022] In a further embodiment the fabric structure also has elastic
and/or regular non-elastic multifilament and/or quasi-multifilament
threads in addition to monofilament threads. By choosing the individual
threads the filtration properties of the filter cloth can be changed
selectively. However in order to obtain a fabric with good abrasive
properties it may be advantageous to design the fabric structure
in this case in such a way that at least one surface of the filter
cloth is constituted in a substantially complete manner by monofilament
threads.
[0023] In the case of applications which show an increased tendency
to fabric clogging, for instance in suspensions containing a high
proportion of very small particles, a filter cloth is preferred
that is designed in its entirety of monofilament threads. Here the
fabric structure may be designed completely of highly elastic monofilament
threads or it may also consist to a certain degree of regular, non-elastic
monofilament threads in addition to the elastic monofilament threads.
[0024] In a particularly simple embodiment of the invention the
warps of the fabric structure consist of a highly elastic monofilament
thread and the wefts consist of a regular non-elastic thread. A
filter cloth of such type has a strong directional elasticity which
is of advantage in the use as a filter band for example.
[0025] The fabrics are preferably produced in twill and/or satin
weaves, wherein highly elastic monofilament threads can be used
in the warp and/or weft direction.
[0026] If specific mechanical properties of the filter cloth and/or
specific filtration properties are required, double and multilayer
fabrics in various fabric textures are also possible. In combining
elastic and regular monofilament threads in all fabric directions
and/or alternately in a particular direction any chosen elasticity
profile can be produced.
[0027] Finally, considerably improved removing properties of the
filter cloth for the filter cake can be achieved in that a surface
of the filter cloth, in particular the surface of a side directed
towards a filter cake, is calendered and/or provided with a coating
for refining the surface. In addition, the monofilament threads
can also be provided with an additional anti-adhesive coating.
[0028] The object set out above is solved with regard to the filter
bag by a filter bag for disk filters, which is produced of a filter
cloth according to the invention.
[0029] As far as the filter bag according to the invention is concerned
in particular the advantage of the balloon effect and the related
fulling effect is of importance, with these effects being intensified
to a great extent by the use of highly elastic monofilament threads
according to the invention. With these highly elastic monofilament
threads very great extensions can already be achieved whilst applying
little force so that for instance great surface extensions can be
achieved with small blasts of compressed air. For example in the
filter bag according to the invention surface extensions amounting
to .DELTA.A/A.gtoreq.0.02 are possible. The bag is fabricated in
a disk-segment shaped manner. On account of the elastic material
the narrow opening at the bottom of the bag can be pulled onto the
segment frame whilst still resting properly on the supporting surface.
[0030] By preference, the invention can be applied to filters employed
for a cake-forming filtration, in which a device for blowing off
the filter cake from the rear of the filtration area is provided.
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